This disclosure relates to seismic surveys and seismic sources, including marine-based seismic source deployment. More generally, the disclosure encompasses deployment and retrieval technologies for marine-based seismic source systems, including, but not limited to, towed air gun arrays.
Traditional marine seismic surveys typically utilize a number of seismic source and receivers systems towed behind a seismic survey vessel, for example in the form of an air gun array and a towed seismic streamer array. Alternatively, a combination of seismic sources can be employed with one or more ocean bottom cables or autonomous node systems, e.g., as described in one or more of Gagliardi et al., U.S. Pat. No. 8,593,905, MARINE SEISMIC SURVEYING IN ICY OR OBSTRUCTED WATERS, issued Nov. 26, 2013; Lambert et al., U.S. Pat. No. 8,730,766, SEISMIC SYSTEM WITH GHOST AND MOTION REJECTION, issued May 20, 2014; Rigsby et al., U.S. Pat. No. 9,121,969, POWER SAVINGS MODE FOR OCEAN BOTTOM SEISMIC DATA ACQUISITION SYSTEMS, issued Sep. 1, 2015; Roberts et al., U.S. Pat. No. 9,354,343, DECLINATION COMPENSATION FOR SEISMIC SURVEY, issued May 31, 2016; and Gagliardi, et al., U.S. Pat. No. 9,535,182, MARINE SEISMIC SURVEYING WITH TOWED COMPONENTS BELOW WATER SURFACE, issued Jan. 3, 2017; each of which is incorporated by reference herein, in the entirety and for all purposes.
Seismic exploration techniques include controlling the emission of seismic energy directed into the Earth with a seismic source (e.g., dynamite, air guns, vibrators, etc.), and monitoring the Earth's response to the seismic energy with one or more nodes or receivers configured to detect reflected seismic waves, in order to create an image of the subsurface. In operation of a typical seismic survey, the air guns or other sources are used to generate seismic energy in the form of acoustic waves, which propagates down through the water column, penetrates the ocean floor or other bottom surface, and is reflected from the underlying subsurface structures. The reflected energy travels back up to the seismic streamers, nodes, or other seismic receivers, where it is detected by hydrophones, geophones and similar seismic sensor devices configured to generate seismic data responsive to the seismic waveforms. Scientists and engineers can then conduct seismic surveys based on the acquired sensor data, e.g., utilizing seismic inversion and other wave exploration techniques, in order to identify and map oil and gas reservoirs, salt and rock formations, and other subsurface structures of interest.
Conventional marine seismic surveys generally involve towing one or more seismic sources behind a seismic vessel, along with an array of seismic receivers or nodes. The seismic nodes can deployed along one or more ocean bottom cables, in the form of autonomous nodes disposed on the seabed, or deployed at a particular depth and orientation within the water column. Each receiver or node can include a number of different pressure and/or particle motion sensors in proximity to one another, for example using a hydrophone system that records scalar pressure measurements of the seismic wavefield and a geophone array that records three-dimensional vector velocity measurements of the corresponding particle motion. Geophysical data pertaining to the wavefield can then be acquired by observing the reflected seismic signals, and the signals can be processed to form an image indicating the composition and subsurface structure of the Earth near the survey location, as described above.
Deploying, towing and retrieving the seismic sources are complex tasks, limiting the number of conventional source configurations that can be used in a given survey area. As more air guns or other sources are added to the array, the associated high-pressure pneumatic connections and umbilical cabling also get longer and larger in diameter, increasing drag, turbulence and vibrational effects. Increased drag consumes more fuel and can slow the tow vessel, substantially raising operational costs. As a result, there is a need for a more flexible approach to source towing and seismic source array deployment, which is not subject to all the same limitations of the prior art.